Birch Double Hook Bra Extender 30mm

Bra Size Guide

Up to 80% of women wear the wrong bra size. Measuring at home takes less than 5 minutes — all you need is a soft tape measure.

Step 1 — Band Size (Underbust)

Wrap the tape firmly around your ribcage, directly under your bust. Snug but not tight.

Measurement (cm)	AU Band
63–67cm	10
68–72cm	12
73–77cm	14
78–82cm	16
83–87cm	18
88–92cm	20
93–97cm	22
98–102cm	24
103–107cm	26

Step 2 — Bust (Fullest Point)

Measure around the fullest part of your bust, tape parallel to the floor. Don’t pull tightly.

Step 3 — Cup Size

Subtract band measurement from bust measurement. The difference is your cup size.

Difference	Cup	Difference	Cup
<1cm	AA	15–16cm	FF
1–2cm	A	17–18cm	G
3–4cm	B	19–20cm	GG
5–6cm	C	21–22cm	H
7–8cm	D	23–24cm	HH
9–10cm	DD	25–26cm	J
11–12cm	E	27–28cm	JJ
13–14cm	F	29cm+	K

Example: Underbust 78cm = band 16. Bust 91cm − 78cm = 13cm = F cup. Your size is 16F.

How to Check the Fit

• Band: sits horizontal, two fingers fit under. Provides 80% of support.
• Cups: all tissue inside, no spillage or wrinkling.
• Straps: comfortable, not digging in or slipping.
• Centre gore: lies flat against sternum.

Common Problems

Problem	Fix
Band riding up	Go down a band, up a cup
Straps digging in	Tighten or go down a band
Underwire poking	Go up a cup
Cups wrinkling	Go down a cup
Tissue spilling	Go up a cup
Gore not flat	Go up a cup

Read the full size guide →